The present invention is directed to a data processing system in which a plurality of mutually asynchronous data handling devices are in communication with a host processor for processing data transmitted over a common bus system and more particularly to a communication adapter for processing interrupt messages from a plurality of remote terminal devices independently of the operation of the host processor.
Present data processing systems have included a central or host processor and a plurality of data handling peripheral units which are connected to the host processor for the purpose of exchanging information with the host processor. Since each of the peripheral units operates independently of each other, conflicts can arise between a plurality of peripheral units trying to gain access to the host processor at the same time. Where the host processor has unlimited processing capability to handle all the requests generated by the peripheral units, this condition presents very few problems. But when for various cost-related reasons, the host processor has limited memory capacity, storage facilities, communicaton ports, etc., it is necessary to provide other means to allow the host processor to effectively function in this environment without limiting its operation.
The most common solution to this problem is to insert a communication adapter between the host processor and the peripheral devices allowing the adapter to handle all communication requests from a plurality of assigned peripheral devices with the host processor communicating only with the adapters. An example of this type of system is disclosed in U.S. Pat. No. 3,254,038 issued to Stafford in which the central processor polls each of the adapters to determine if they contain any messages from their assigned peripheral devices. The drawback of this system is in the cost of the adapters and the fact that the central processor is required to poll each of the adapters thereby requiring a considerable amount of software in the central processor's program to provide a polling sequence which is quite costly and time consuming. In U.S. Pat. No. 4,039,757 issued to Frisone, the adapter is constructed to connect a plurality of remote devices directly to the central processor in response to the polling of the adapter by the central processor. Again, the processor is required to provide the software support polling program with respect to the adapters which slows down the processing operation.
Accordingly, it is an object of the present invention to provide a low-cost adapter for processing interrupt messages between a plurality of remote peripheral devices and a host processor without requiring the host processor to generate a polling sequence operation with respect to the remote peripheral devices. It is another object of this invention to provide an adapter for processing interrupt messages from a plurality of remote peripheral devices which is hardware orientated rather than software orientated. It is another object of this invention to provide an adapter with a microprocessor which communicates with a requesting remote peripheral device without going through a polling sequence.